Copy the above code to some C file (For eg. tty-send-command.c). Run the following command in the directory you have created the C file in to compile the code.

make tty-send-command

Copy this file to the bin directory.

Start another terminal or switch to any other open terminal that you wish to control and execute the command tty. You can see a sample output below.

@~$ tty
/dev/pts/4

Now to execute a command on /dev/pts/4, run the following command in the controlling/original terminal.

sudo tty-send-command -n /dev/pts/4 echo "Hello there"

You will see that the ls command is executed in /dev/pts/4. The -n option makes tty-send-command send a newline after the command, so that the command gets executed and not just inserted. This utility can infact be used to send any data to other terminals For eg, you could open vim in /dev/pts/4 and then run the following command in the controlling terminal to cause vim to exit in /dev/pts/4.

sudo tty-send-command -n /dev/pts/4 :q

To avoid using sudo all the time, so that the command is easily scriptable, change the owners/permissions of this executable using the following commands.

sudo chown root:root tty-send-command
sudo chmod u+s tty-send-command

What we did was change the owner/group to root and set the setuid bit for the executable which will allow you to run the utility with root permissions.

If you are running a mission critical server, or maintaining a storage server loaded with sensitive data, you probably want to closely monitor file access activities within the server. For example, you want to track any unauthorized change in system configuration files such as /etc/passwd.

To monitor who changed or accessed files or directories on Linux, you can use the Linux Audit System which provides system call auditing and monitoring. In the Linux Audit System, a daemon called auditd is responsible for monitoring individual system calls, and logging them for inspection.

In this tutorial, I will describe how to monitor file access on Linux by using auditd.

To install auditd on Debian, Ubuntu:

$ sudo apt-get install auditd

Once installed by apt-get, auditd will be set to start automatically upon boot.

To install auditd on Fedora, CentOS or RHEL:

$ sudo yum install audit

If you want to start auditd automatically upon boot on Fedora, CentOS or RHEL, you need to run the following.

$ sudo chkconfig auditd on

Once you installed auditd, you can configure it by two methods. One is to use a command-line utility called auditctl. The other method is to edit the audit configuration file located at /etc/audit/audit.rules. In this tutorial, I will use the audit configuration file.

Once auditd starts running, it will start generating an audit daemon log in /var/log/audit/audit.log as auditing is in progress.

A command-line tool called ausearch allows you to query audit daemon logs for specific violations.

To check if a specific file (e.g., /etc/passwd) has been accessed by anyone, run the following. As shown in the above example audit configuration, auditd checks if /etc/passwd is modified or tampered with using chmod.

What is vi?

The default editor that comes with the UNIX operating system is called vi (visual editor). [Alternate editors for UNIX environments include pico and emacs, a product of GNU.]

The UNIX vi editor is a full screen editor and has two modes of operation:

Command mode commands which cause action to be taken on the file, and

Insert mode in which entered text is inserted into the file.

In the command mode, every character typed is a command that does something to the text file being edited; a character typed in the command mode may even cause the vi editor to enter the insert mode. In the insert mode, every character typed is added to the text in the file; pressing the <Esc> (Escape) key turns off the Insert mode.

While there are a number of vi commands, just a handful of these is usually sufficient for beginning vi users. To assist such users, this Web page contains a sampling of basic vi commands. The most basic and useful commands are marked with an asterisk (* or star) in the tables below. With practice, these commands should become automatic.

NOTE: Both UNIX and vi are case-sensitive. Be sure not to use a capital letter in place of a lowercase letter; the results will not be what you expect.

To Get Into and Out Of vi

To Start vi

To use vi on a file, type in vi filename. If the file named filename exists, then the first page (or screen) of the file will be displayed; if the file does not exist, then an empty file and screen are created into which you may enter text.

*

vi filename

edit filename starting at line 1

vi -r filename

recover filename that was being edited when system crashed

To Exit vi

Usually the new or modified file is saved when you leave vi. However, it is also possible to quit vi without saving the file.

Note: The cursor moves to bottom of screen whenever a colon (:) is typed. This type of command is completed by hitting the <Return> (or <Enter>) key.

*

:x<Return>

quit vi, writing out modified file to file named in original invocation

:wq<Return>

quit vi, writing out modified file to file named in original invocation

:q<Return>

quit (or exit) vi

*

:q!<Return>

quit vi even though latest changes have not been saved for this vi call

Moving the Cursor

Unlike many of the PC and MacIntosh editors, the mouse does not move the cursor within the vi editor screen (or window). You must use the the key commands listed below. On some UNIX platforms, the arrow keys may be used as well; however, since vi was designed with the Qwerty keyboard (containing no arrow keys) in mind, the arrow keys sometimes produce strange effects in vi and should be avoided.

If you go back and forth between a PC environment and a UNIX environment, you may find that this dissimilarity in methods for cursor movement is the most frustrating difference between the two.

In the table below, the symbol ^ before a letter means that the <Ctrl> key should be held down while the letter key is pressed.

*

jor<Return>
[or down-arrow]

move cursor down one line

*

k [or up-arrow]

move cursor up one line

*

hor<Backspace>
[or left-arrow]

move cursor left one character

*

lor<Space>
[or right-arrow]

move cursor right one character

*

0 (zero)

move cursor to start of current line (the one with the cursor)

*

$

move cursor to end of current line

w

move cursor to beginning of next word

b

move cursor back to beginning of preceding word

:0<Return> or 1G

move cursor to first line in file

:n<Return> or nG

move cursor to line n

:$<Return> or G

move cursor to last line in file

Screen Manipulation

The following commands allow the vi editor screen (or window) to move up or down several lines and to be refreshed.

^f

move forward one screen

^b

move backward one screen

^d

move down (forward) one half screen

^u

move up (back) one half screen

^l

redraws the screen

^r

redraws the screen, removing deleted lines

Adding, Changing, and Deleting Text

Unlike PC editors, you cannot replace or delete text by highlighting it with the mouse. Instead use the commands in the following tables.

Perhaps the most important command is the one that allows you to back up and undo your last action. Unfortunately, this command acts like a toggle, undoing and redoing your most recent action. You cannot go back more than one step.

*

u

UNDO WHATEVER YOU JUST DID; a simple toggle

The main purpose of an editor is to create, add, or modify text for a file.

Inserting or Adding Text

The following commands allow you to insert and add text. Each of these commands puts the vi editor into insert mode; thus, the <Esc> key must be pressed to terminate the entry of text and to put the vi editor back into command mode.

*

i

insert text before cursor, until <Esc> hit

I

insert text at beginning of current line, until <Esc> hit

*

a

append text after cursor, until <Esc> hit

A

append text to end of current line, until <Esc> hit

*

o

open and put text in a new line below current line, until <Esc> hit

*

O

open and put text in a new line above current line, until <Esc> hit

Changing Text

The following commands allow you to modify text.

*

r

replace single character under cursor (no <Esc> needed)

R

replace characters, starting with current cursor position, until <Esc> hit

cw

change the current word with new text,
starting with the character under cursor, until <Esc> hit

-----------------------------------------------
DISPLAY and MONITORING
-----------------------------------------------
vxdisk list
List all disks used by Veritas (VX).
vxdisk list <diskname>
Display detailed information about a
single disk, including mutlipathing
information, size, type, Vx version,
and more.
vxprint
Display report style information about
the current status of all Vx componants,
including disks, subdisks, plexes, and
volumes.
vxprint <componant>
Display report style information about
the current status of ONLY the componant
you request. So for instance,
"vxprint vol01" shows information about
all subcomponants of vol01. This works
for plexes, disk groups, etc.
vxprint -hrt
Display detailed information about all
Vx componanats, including stwdith,
ncolumns, offsets, layout type, read-
policy, and more. This is best for
a true picture of your configuration.
vxdg list
Display listing and state information
of all Disk Groups.
vxdg list <diskgroup name>
Display detailed information about
a diskgroup, including flags, version,
logs status, etc.
vxinfo
Display volume status and volume type.
By default, only displays "rootdg",
to display a diffrent Disk Group,
use "vxinfo -g <dgname>".
vxassist maxgrow <volume>
This command will output the maximum size
the volume specified can increased by,
specified in sectors.
--------------------------------------------------
DISK TASKS and COMMANDS
--------------------------------------------------
vxdiskadd <devname>
Adds a disk to Vx by Initializing and Encapsolating
it. Specified by its device name (ex: c0t1d0s2).
NOTE: You'll need to reboot to finalize the
disk addition!
This command, can also be used to add a disk to
a specified disk group. Just follow the prompts.
No reboots needed for changing DG's.
vxedit rename <oldname> <newname>
Rename a Vx disk. Ex: "vxedit rename disk01 disk05"
vxedit set reserve=on <diskname>
Sets the "reserve" flag to a Vx disk. This
is used to keep specific disks from being
accidentally, or generally used.
vxdisk offline <diskname>
Used to "offline" a disk. The disk should
be removed from its diskgroup before being
offlined.
vxdisk rm <devname>
Used to remove disks from Vx control completely.
Ex: "vxdisk rm c0t1d0s2" Make sure to
removed the disk from its diskgroup, and offline
the disk before removing it.
vxedit set spare=on <diskname>
Sets the "spare" flag to a Vx disk. This is used
to make the specified disk a hot spare, which
is then added to the "hot spare pool".
vxedit set spare=off <diskname>
Same as above but removes the disk from the
"hot spare pool".
----------------------------------------------------
DISK GROUPS and COMMANDS
----------------------------------------------------
vxdg init <diskgroup> <diskname>=<devname>
Creates a new disk group, and assigns the naming
scheme to the first disk added to the group.
ex: "vxdg init newdg newdg01=c0t10d0s2".
NOTE: This is kinda tricky because the disk that
you're adding can't be a member of ANY DG, but
must be initialized. It's easier to use
"vxdiskadd", and add the disk to a newdg by
specifying a new DG name for the DG field.
vxdg deport <diskgroup>
Disabled a diskgroup, but doesn't remove it. Often
used as an organized pool of disk to realocate, and
to moved DG's from one system to another.
vxdg import <diskgroup>
Reverse of above. Enables local access to the specified
disk group.
vxdg -n <newdgname> <olddgname>
Change a Disk Groups name.
vxdg list <dgname>
Use this to check the version numbers of Disk
Groups. Shows other details about the DG too.
vxdg destroy <dgname>
Removes the specified DG, and frees all its disks
back to general use by Vx.
-= Quick Chart!: Disk Group Version Number Translation
VxVM Introduced Supported
Release Version Versions
------- ------------ ---------
1.2 10 10
1.3 15 15
2.0 20 20
2.2 30 30
2.3 40 40
2.5 50 50
3.0 60 20-60
-----------------------------------------------------------
SUBDISKS and COMMANDS
-----------------------------------------------------------
vxmake sd <subdiskname> <disk>,<offset>,<length>
Creates a subdisk with the specified name,
and by the offset and length specified.
ex: "vxmake sd disk02-01 disk02,0,8000"
NOTE: If you are going to add this subdisk
to a plex, its good to check the other
subdisks in that plex to see what their
lengths and offsets are, use the command:
"vxprint -st"
vxedit rm <subdiskname>
Removes a subdisk.
vxsd assoc <plexname> <subdiskname>,....
Associates the specified subdisks to
the specified plex. Example:
"vxsd assoc vol01-03 disk01-01,disk02-01"
NOTE: Striped volumes are diffrent,
you need to specify the column# so
use the following:
vxsd -l <col#/offset> assoc <plexname> <subdiskname>,...
Same as above, but used for associating
subdisks to a striped plex. Use the command
"vxprint -st" to see what other subdisk
in the plex look like, and then set the
new subdisks column number and offset
(found in the seventh column of output)
to the appropriate value.
vxsd aslog <plex> <subdiskname>
Adds a log subdisk to the specified plex.
Ex: "vxsd aslog vol01-02 disk03-01"
vxsd dis <subdiskname>
Disassociates the specified subdisk from its
current plex.
------------------------------------------------------
PLEXS and COMMANDS
------------------------------------------------------
vxmake plex <plexname> sd=<subdiskname>,<subdiskname>,....
Creates a new plex by the name specified and
assigns the specified subdisks to it.
vxmake plex <plexname> layout=<layout> stwidth=<stwidth> ncolumn=<ncolumn> sd=...
Like above command, but specifies layout type
as defined by <layout>, which is used for creation
of striped and RAID5 plexes. The layout is
constrained by the defined number of columns,
and stripe width. Subdisks specified are
added to the created plex.
vxplex att <volname> <plexname>
Associates specified plex with specified volume.
(Adds a mirror)
NOTE: Attachment will take a while. Watch
it with Vxtask, or via vxprint
vxplex dis <plexname>
Disassociate specified plex from its connected
volume.
vxedit -r rm <plexname>
Remove the plex.
vxmend off <plexname>
Offlines a plex for repair to it's disks.
vxplex det <plexname>
Detaches specified plex from its connected
volume, but maintians association with it's
volume. The plex is no longer used
for I/O untill it is (re)attached.
vxmend fix clean <plexname>
Used to clean plexes that are in the
"unclean" state. Used with unstartable
volumes.
vxplex mv <originalplex> <newplex>
Moves the data content from the origonal
plex onto a new plex.
NOTE: The old plex must be active (ENABLED).
The new plex should be the same length, or
larger than the old plex. The new plex
must not be associated with another volume.
(duh)
vxplex cp <volume> <newplex>
Copies the data from the specified volume
to a new plex.
NOTE: The new plex cannot be associated
with any other volume. The new plex,
further, will NOT be attached to
the specified volume. (Also, see notes
from above)
-------------------------------------------------------
VOLUMES and COMMANDS
-------------------------------------------------------
vxassist make <volumename> <length>
Creates a new volume with the name specified
and is made to the length specified.
Ex: "vxassist make newvol 10m"
NOTE: This command will pull disk space
from the generally avalible Vx disk space.
vxassist make <volname> <length> layout=<layouttype> <disk> <disk> ....
Like the above command, but with layout specified.
The most common layouts are: striped and raid5
ex: "vxassist make newvol 100m layout=raid5 disk01 disk02 disk03"
NOTE: See the vxassist(1M) man page for more information.
vxmake vol <volname> len=<length> plex=<plexname>,...
Creates a new volume of specified length (usually
in sectors), and attachs the specified plexes to that
volume. Useful for creating volumes to house
copied or moved plexes.
NOTE: See the vxmake(1M) man page for more information.
vxvol init <state> <volname> [plexname]
Manually sets the state of a volume.
NOTE: Not for the squimish.
vxassist maxsize [layout=raid5]
Returns the maximum size avalible via Vx to create
a new volume. By adding "layout=raid5" to the command
the calulations take into account losse due
to raid5. Output is in sectors and Megs.
vxassist maxgrow <volname>
Returns the maximum ammount of Vx space that
can be added to the specified volume.
vxassist mirror <volname>
Creates a mirror for the specified volume.
NOTE: Think of this as "handsfree plex creation".
This is fast, but the disks you want used
may not be used... often best to do manually.
vxassist addlog <volname>
Adds a Dirty Region Log (DRL) for the specified volume.
vxassist remove log <volname>
Reverse of above.
vxvol start <volname>
Starts a volume
vxvol stop <volname>
Stops a volume. Alternately you can use command as
such: "vxvol stopall" in order to stop all volumes.
vxassit growto/growby/shrinkto/shrinkby <volname> <length>
Resizes the volume specified. Use one of the
following: growto, growby, shrinkto, and shrinkby
in order to descide what <length> specifies.
By default length is specified in sectors.
This does not resize the filesystem inside the volume.
NOTE: Don't shrink volumes to be less that
its contained filesystem! (duh)
vxvol set len=<length> <volname>
An alternate to above command. Sets the absolute
lenths of the specified volume to the length
specified, by default, in sectors. This
does not resize the filesystem inside the volume.
NOTE: There is also a resize(1M) command, used
for resizing both volume AND filesytem. See
the man page for that one.
vxedit rm <volname>
Removes the specified volume. (poof!)
NOTE: If the volume specified is in the ENABLED
state, you will need to use the command
"vxedit -f <volname>". Also, using the "r"
with "f" will remove all plexes and subdisks
with the volume. If you didn't guess, "r"
is Recursive, and "f" is Force.
----------------------------------------------------------------
Misc Stuff:
To calculate the size of a filesystem inside a volume, use
the command:
fstyp -v <volume-device-path> | head -30 | grep ncg
Ignore the errors. Output will look this this:
# fstyp -v /dev/vx/rdsk/datadg/vol01 | head -30 | grep ncg
ncg 17152 size 70254592 blocks 65863396
# Broken Pipe
Unknown_fstyp (no matches)
The size found after the label "size" is presented in kilobytes.
You can convert to sectors by multiplying by 2.
-----------
To calculate the size of a volume, use vxprint, and look for the
"len". The volume length is in sectors. Convert to kilobytes
by dividing by 2.
-------------
Volume Growth Procudure:
1) You can use vxassist to estimate the max size of
a given volume based on the disks you wish to add:
ex: # vxassist -g rootdg maxgrow vol01 disk01 disk02 disk03
2) Next, actually grow the volume (NOT THE FS) via the
command (assuming maxgrow outputed 10639360 as the maxsize):
ex:# vxassist -g rootdg growto vol01 10639360 disk01 disk02 disk03
3) Now VxVM grinds away, monitor with vxtask.
4) Now Grow the Filesystem, for UFS use:
# /usr/lib/fs/ufs/mkfs -F ufs -M /export /dev/vx/rdsk/rootdg/vol01 10639360
for VXFS ufs:
# /usr/lib/fs/vxfs/fsadm -b 10639360 -r /dev/vx/rdsk/rootdg/vol01 /mnt
---------------------------------------------------------------
5) Done!
----------
Changing User/Group of a Raw Volume: (ex:)
vxedit -g xxxdg set group=dba data_vol_123vxedit -g xxxdg set user=oracle data_vol_123

This post will cover how to increase the disk space for a VMware virtual machine running Linux that is using logical volume manager (LVM). Firstly we will add a new disk to the virtual machine and then extend the original LVM over this additional space. Basically we will have two physical disks but just one volume group and one logical group that is using the space on both disks together. With this method there is no down time for the virtual machine.

As there are a number of different ways to increase disk space I have also posted some different methods here:

Important Notes: Be very careful when working with the commands in this article as they have the potential to cause a lot of damage to your data. If you are working with virtual machines make sure you take a snapshot of your virtual machine beforehand, or otherwise have some other form of up to date backup before proceeding. It could also be worth cloning the virtual machine first and testing out this method on the clone.

Throughout my examples I will be working with a VMware virtual machine running Debian 6, this was set up with a 20gb disk and we will be adding a new 20gb disk for a total LVM size of 40gb.

Although my examples make use of virtual machines, this method would work with a physical server as well if you have added a new physical disk in and want to use that to expand the LVM.

Identifying the partition type

As this method focuses on working with LVM, we will first confirm that our partition type is actually Linux LVM by running the below command.

fdisk -

As you can see in the above image /dev/sda5 is listed as “Linux LVM” and it has the ID of 8e. The 8e hex code shows that it is a Linux LVM, while 83 shows a Linux native partition. Now that we have confirmed we are working with an LVM we can continue.

Below is the disk information showing that our initial setup only has the one 20gb disk currently, which is under the logical volume named /dev/mapper/Mega-root – this is what we will be expanding with the new disk.

Note that /dev/mapper/Mega-root is the volume made up from /dev/sda5 currently – this is what we will be expanding.

Adding a new virtual hard disk

First off we add a new disk to the virtual machine. This is done by right clicking the virtual machine in vSphere, selecting edit settings and then clicking the “Add…” button which is used to add hardware to the virtual machine.

Select hard disk and click next.

Select create a new virtual disk and click next.

Select the disk size you want to add, I will be using 20gb as previously mentioned. I have also selected to store the disk with the virtual machine, it will store on the same datastore as the virtual machines files, this will be fine for my test purposes. Click next once complete.

Select next on the advanced options page.

Review everything and click finish once you have confirmed the settings.

You will then see the new disk under the hardware devices tab and it will be labelled with (adding) which means it will not apply until you click OK, so click OK to complete the process.

Detect the new disk space

In my test for this example, as soon as I added the additional disk in through VMware it displayed through “fdisk -l” for me, you can see the second disk labelled /dev/sdb (I have cropped out the information on /dev/sda1 to make it less cluttered here). It is also worth noting that it shows as not containing a valid partition table, we are about to set this up.

This may not however be the case for you, to avoid reboot you may need to rescan your devices, you can try this with the below command. Note that you may need to change host0 depending on your setup.

echo "- - -" > /sys/class/scsi_host/host0/scan

If you have issues detecting the new disk, just perform a reboot and it should then display correctly.

Partition the new disk

We now need to partition the new /dev/sdb disk so that it can be used, this is done by using fdisk.

fdisk /dev/sdb

This should provide us with the below prompt, the inputs I have entered in are shown in bold.

‘n’ was selected for adding a new partition.

root@Mega:~# fdisk /dev/sdb
Command (m for help): n

‘p’ is then selected as we are making a primary partition.

Command action
e extended
p primary partition (1-4)
p

As this is a new disk, we do not yet have any partitions on it so we will use partition 1 here.

Partition number (1-4): 1

Next we press the enter key twice, as by default the first and last cylinders of the unallocated space should be correct.

Now we need to confirm the name of the current volume group using the vgdisplay command. The name will vary depending on your setup, for me it is the name of my test server. vgdisplay provides plenty of information on the volume group, I have only shown the name and the current size of it for this example.

Next we need to increase the logical volume with the lvextend command (rather than the physical volume which we have already done). This means we will be taking our original logical volume and extending it over our new disk/partition/physical volume of /dev/sdb1.

Firstly confirm the name of the logical volume using lvdisplay. The name will vary depending on your setup.

If you like you can then run vgdisplay and lvdisplay again to confirm the size of the volume group and logical volume respectively, I have done this and I now have the following.

LV Size 38.90 GiB
VG Size 39.75 GiB

However if you run a “df” command to see available disk space it will not have changed yet as there is one final step, we need to resize the file system using the resize2fs command in order to make use of this space.